THE Pentagon's efforts to develop a beam weapon that can deter an adversary by causing a burning sensation on their skin has taken a step forward with the development of a small, potentially hand-held, version. The weapon, which is claimed to cause no permanent harm, could also end up being used by police to control civilians.

"But the exact operating irradiance which balances a useful military effect with a conservative margin of safety has not been nailed down yet."That's something that will have to be done before the weapon is deployed, as too powerful a laser beam could permanently blind someone if fired at their eyes

The Pentagon already has a large crowd control weapon called theActive Denial Systemthat can heat whole groups of people, causing them to flee. It uses a flat-plate antenna mounted on a truck or aircraft to aim a 2-metre-wide microwave beam at the crowd.

Like all supposedly non-lethal weapons that could be used to control civilians, the Pentagon's new portable weapon is raising concerns. "I'd like to know why they want another advanced pain compliance weapon like this,"